The t-butoxycarbonyl radical (Bu^tOĊO), produced by photolysis of di-t-butyl peroxide in the presence of t-butyl formate, has been observed by e.s.r. spectroscopy and shown to be a σ-radical; the kinetics of the decarboxylation of Bu^tOĊO have been measured and the reaction shown to have a low A-factor (10^10·8s^–1) for a unimolecular scission.